1. Field of the Invention
This invention relates in general to methods for treating sewer sludge, or a mixture of sewer sludge and municipal solid waste, to produce landfill daily cover, general ground cover, or other type biosolids.
2. Prior Art
Sewer sludge, the residue generated during treatment of domestic sewage, has beneficial plant nutrients and soil conditioning properties. However, it may also contain pathogenic bacteria, viruses, protozoa, parasites, and other microorganisms that can cause disease. For this reasons most industrialized countries, including the United States, regulate the ways in which sewer sludge can be disposed. Under these regulations sewer sludge must be treated to reduce the risk of disease from the pathogens in the sewer sludge, as well as reduces the odor problems caused by sewer sludge.
Because of the current high cost of treatment of sewer sludge to permit its use on land having a high potential for public exposure, such as use on lawns, golf courses and similar uses, the most common method for handling disposal of municipal solid waste and sewer sludge is through disposal in landfills. However, even this use of sewer sludge faces environmental regulatory requirements that impact the cost to dispose of sewer sludge through use of landfills. One such regulation designed to reduce environmental concerns relating to landfills is the EPA mandated recycling quotas; i.e., the amount of material the landfill is allowed to take in each day depends upon the percent of the material that can be recycled. Thus, a certain portion of the sewer sludge must be treated in a manner that permits it to be recycled for uses other than landfill in order that a landfill can accommodate the constant daily flow of new incoming sewer sludge. To meet the recycling requirements is expensive, and requires in most cases large capital investments in special container and trucks, as well as increased operating costs. Methods to reduce the costs associated with these recycling requirements would be a significant benefit to the landfill operators.
Another particular problem encountered by landfill operators is the handling of sewer sludge that is to be disposed in the landfill. Typically sewer sludge makes up 10% of the material received daily by a landfill for disposal. Sewer sludge often contains as much as 70% water and has to be de-watered before it can be disposed in the landfill. In addition, because of the composition of sewer sludge significant odor problems occur. Still further, because sewer sludge is not easily packed it sticks to the equipment located at the landfill that results in further odor problems. Methods that can treat the sewer sludge that more easily and less expensively make it suitable for disposal in the landfill, as well as minimize the odor problems would be a significant benefit to the landfill operators.
A third problem encountered in the operation of landfills is the regulatory requirement that each day the newly deposited material disposed in the landfill must be covered with material meeting EPA requirements. This material is commonly referred to in the industry as daily cover. At present most landfills utilize soil that in many cases has to be trucked in and then spread over the newly deposited material. Under current regulations the use of soil requires that a six inch layer of soil be used to cover the sewer sludge that has been disposed in the landfill each day. Alternatively, ground cellulose containing flame retardant can be used. In some landfills a tarpaulin is rolled over the newly deposited material at the end of each day and then rolled back at the beginning of the next day. Each of these methods is expensive. Less expensive solutions to this problem would also be of significant benefit to the landfill operators.